A discharge lamp lighting device (a high-pressure discharge lamp lighting device) has heretofore been proposed which is used for lighting a high-pressure discharge lamp (also referred to as a high-intensity discharge lamp or a HID lamp) such as a metal halide lamp or a high-pressure mercury lamp.
As shown in FIG. 1, a high-pressure discharge lamp lighting device of this type includes a rectifier 100 such as a diode bridge that performs full-wave rectification of an alternating electric current supplied from an alternating current power source AC, a step-up chopper circuit 110 that steps up an output voltage from the rectifier 100 to a prescribed value, a smoothing capacitor 120 that smoothes an output voltage from the step-up chopper circuit 110, a step-down chopper circuit 130 that steps down the output voltage from the step-up chopper circuit 110 to a prescribed value, a smoothing capacitor 140 that smoothes an output voltage from the step-down chopper circuit 130, an inverter circuit 150 that converts a direct electric current outputted from the step-down chopper circuit 130 into a square wave alternating current (a square wave alternating electric current) whose polarity is inverted at a prescribed frequency, and supplies the square wave alternating current to a high-pressure discharge lamp DL, an igniter 160 that applies a starting voltage to the high-pressure discharge lamp DL, and a controller 170 that controls operations of the respective circuits.
In the device shown in FIG. 1, the step-up chopper circuit 110 includes an inductor 111, a switching element 112, and a diode 113. The step-down chopper circuit 130 includes a switching element 131, an inductor 132, and a diode 133. The inverter circuit 150 is a full-bridge circuit which includes four switching elements 151 to 154. The controller 170 lights the high-pressure discharge lamp DL by performing on-off control of the switching element 112 in the step-up chopper circuit 110, the switching element 131 in the step-down chopper circuit 130, and the switching elements 151 to 154 in the inverter circuit 150.
If the alternating current power source AC stops supplying the power to the high-pressure discharge lamp lighting device shown in FIG. 1, the voltage between two terminals of the smoothing capacitor 120 drops. When the voltage drops to a certain level, the high-pressure discharge lamp DL cannot continue to be lit any more, and is extinguished.
As described previously, the high-pressure discharge lamp DL is a metal halide lamp, a high-pressure mercury lamp or the like. In the high-pressure discharge lamp DL of this type, arc discharge is initiated after glow discharge, and a lamp voltage thereafter becomes almost constant when a temperature inside an arc tube becomes uniform and stabilized. The high-pressure discharge lamp DL is lit by way of the process described above. Thus, once the lamp DL is extinguished, it is not possible to restart (resume lighting) until the temperature and pressure inside the arc tube are decreased (taking 5 to 15 minutes usually).
Therefore, once the lamp DL is extinguished, it takes time to restart the lamp DL even in a case of a power failure of only a short period (for 10 to 20 ms), such as an instantaneous power failure or an instantaneous voltage drop of the alternating current source AC due to a lightening strike, a start of large electric equipment in the neighborhood, a short-circuit accident, and the like.
One of conceivable methods for solving this problem is to increase a capacity of the smoothing capacitor 120 so that the smoothing capacitor 120 can supply sufficient power to the high-pressure discharge lamp DL during an instantaneous power failure.
However, the increase in the capacity of the smoothing capacitor 120 leads to increases in size, costs, weight, and the like of the high-pressure discharge lamp lighting device. Such increases cannot meet recent market demands for reducing the size, costs, and weight of high-pressure discharge lamp lighting devices.
Accordingly, in order to prevent extinction of the high-pressure discharge lamp DL attributable to an instantaneous power failure or an instantaneous voltage drop without increasing the capacity of the smoothing capacitor 120, there have been proposed techniques to prevent extinction of the high-pressure discharge lamp DL by reducing electrical energy supplied to the high-pressure discharge lamp DL and thereby suppressing power consumption upon occurrence of the instantaneous power failure or the instantaneous voltage drop (see Patent Documents 1 and 2, for example). Here, an amount of power supply to the high-pressure discharge lamp DL is decreased by reducing the output voltage from the step-down chopper circuit 130 in Patent Document 1, and by reducing the output voltage from the step-up chopper circuit 110 in Patent Document 2.